M
Statistically Toleranced Dimensions
We are early days with a new end user and amongst the numerous customer background documents is the requirement for Key Characteristics to be controlled in a slightly different way to our norm.
Fortunately there are no Keys specified up to date, but I thought I had better understand it for the, hopeful, future business. But before I go back to them and look ignorant, I thought I would rather look ignorant to the Covers as you are bound to know the answer or if I am on the right track!
The requirement is that the “Target Value and Acceptable Range should be expressed in terms of a Mean, Standard Deviation and acceptable Sigma Level requirements”.
My best interpretation is:-
Assume a maximum Sigma level could be Design Tolerance/12
Assuming a 4 sigma Level, 1.33 then the Mean would need to be within 2 sigma of target.
Assume a feature was designed to be at 75.00 plus/minus 0.25mm.
Maximum Sigma = 0.50/12 = 0.0417.
So the actual drawing dimension feature would need to be shown as:-
Mean 74.917-75.083
Sigma Max 0.0417.
Cpk Min 1.33
Comments?
Martin in England
Getting Older but no wiser
We are early days with a new end user and amongst the numerous customer background documents is the requirement for Key Characteristics to be controlled in a slightly different way to our norm.
Fortunately there are no Keys specified up to date, but I thought I had better understand it for the, hopeful, future business. But before I go back to them and look ignorant, I thought I would rather look ignorant to the Covers as you are bound to know the answer or if I am on the right track!
The requirement is that the “Target Value and Acceptable Range should be expressed in terms of a Mean, Standard Deviation and acceptable Sigma Level requirements”.
My best interpretation is:-
Assume a maximum Sigma level could be Design Tolerance/12
Assuming a 4 sigma Level, 1.33 then the Mean would need to be within 2 sigma of target.
Assume a feature was designed to be at 75.00 plus/minus 0.25mm.
Maximum Sigma = 0.50/12 = 0.0417.
So the actual drawing dimension feature would need to be shown as:-
Mean 74.917-75.083
Sigma Max 0.0417.
Cpk Min 1.33
Comments?
Martin in England
Getting Older but no wiser